This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:                3GPP third generation partnership project        AP access point        BW bandwidth        CC component carrier        CDM code division multiplexing        C-RNTI cell radio network temporary identity        DL downlink (eNB towards UE)        eNB E-UTRAN Node B (evolved Node B)        EPC evolved packet core        E-UTRAN evolved UTRAN (LTE)        HARQ hybrid automatic repeat request        HO handover        IMT-A international mobile telephony-advanced        ITU international telecommunication union        ITU-R ITU radiocommunication sector        LTE long term evolution of UTRAN (E-UTRAN)        MAC medium access control (layer 2, L2)        MAC-I message authentication code for data integrity of messages        MM/MME mobility management/mobility management entity        Node B base station        O&M operations and maintenance        OFDMA orthogonal frequency division multiple access        PCI physical cell identity        PDCP packet data convergence protocol        PHY physical (layer 1, L1)        RLC radio link control        RRC radio resource control        RRM radio resource management        SC-FDMA single carrier, frequency division multiple access        S-GW serving gateway        UE user equipment, such as a mobile station or mobile terminal        UL uplink (UE towards eNB)        UTRAN universal terrestrial radio access network        
The specification of a communication system known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE or as E-UTRA) is currently nearing completion within the 3GPP. As specified the DL access technique is OFDMA, and the UL access technique is SC-FDMA.
One specification of interest is 3GPP TS 36.300, V8.12.0 (2010-04), “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E UTRA) and Evolved Universal Terrestrial Access Network (E UTRAN); Overall description; Stage 2 (Release 8),” incorporated by reference herein in its entirety. This system may be referred to for convenience as LTE Rel-8 (which also contains 3G HSPA and its improvements). In general, the set of specifications given generally as 3GPP TS 36.xyz (e.g., 36.211, 36.311, 36.312, etc.) may be seen as describing the Release 8 LTE system. More recently, Release 9 versions of at least some of these specifications have been published including 3GPP TS 36.300, V9.9.0 (2011-12), incorporated by reference herein in its entirety, and Release 10 versions of at least some of these specifications have been published including 3GPP TS 36.300, V10.6.0 (2011-12), incorporated by reference herein in its entirety. Even more recently, Release 11 versions of at least some of these specifications have been published including 3GPP TS 36.300, V11.0.0 (2011-12), incorporated by reference herein in its entirety.
FIG. 1 reproduces FIG. 4-1 of 3GPP TS 36.300, and shows the overall architecture of the E-UTRAN system. The E-UTRAN system includes eNBs, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE (not shown). The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to an EPC, more specifically to a MME (Mobility Management Entity) by means of a S1 MME interface and to a Serving Gateway (SGW) by means of a S1 interface. The S1 interface supports a many-to-many relationship between MMEs/S-GW and eNBs.
The eNB hosts the following functions:                functions for RRM: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both UL and DL (scheduling);        IP header compression and encryption of the user data stream;        selection of a MME at UE attachment;        routing of User Plane data towards the Serving Gateway;        scheduling and transmission of paging messages (originated from the MME);        scheduling and transmission of broadcast information (originated from the MME or O&M); and        a measurement and measurement reporting configuration for mobility and scheduling.        
Of particular interest herein are the further releases of 3GPP LTE (e.g., LTE Rel-10) targeted towards future IMT-A systems, referred to herein for convenience simply as LTE-Advanced (LTE-A). Reference in this regard may be made to 3GPP TR 36.913, V8.0.1 (2009 03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Requirements for Further Advancements for E UTRA (LTE-Advanced) (Release 8), incorporated by reference herein in its entirety. A goal of LTE-A is to provide significantly enhanced services by means of higher data rates and lower latency with reduced cost. LTE-A is directed toward extending and optimizing the 3GPP LTE Rel-8 radio access technologies to provide higher data rates at very low cost. LTE-A will most likely be part of LTE Rel-10. LTE-A will be a more optimized radio system fulfilling the ITU-R requirements for IMT-A while maintaining backward compatibility with LTE Rel-8. Reference is further made to a Release 9 version of 3GPP TR 36.913, V9.0.0 (2009-12), incorporated by reference herein in its entirety. Reference is also made to a Release 10 version of 3GPP TR 36.913, V10.0.0 (2011-06), incorporated by reference herein in its entirety.
In LTE system, if the UE loses a radio frequency (RF) connection to an access point (AP) (for example, an eNB, a relay node, etc.), the UE may use an RRC Reestablishment procedure to establish the RF connection. The UE is allowed to use the RRC Reestablishment procedures in the following scenarios inter-eNB (Intra/Inter cell) reestablishment and inter-eNB reestablishement when the UE uses the source cell C-RNTI and attempt the RRC Reestablishment procedures in a prepared/alternate cell.
FIG. 2 illustrates an exemplary handover situation. As shown the UE 220 is located within a source cell 215 served by source eNB 210 and a target cell 235 served by target eNB 230. In this situation, the UE 220 is connected to the source cell 215 and is being handed over to the target cell 235. As shown, UE 220 is on the edge of target cell 235 (e.g., on the eNB seam). During the handover procedure, UE 220 may lose the connection to the target cell 235. After an unsuccessful inter-eNodeB handover, the UE may attempt to return to the source eNB 210 (or ping-pong).
During the handover procedure, the UE 220 is configured for operation in the target cell 235. However, if the connection is lost certain messages may not be received by the UE 220. In these situations, the UE 220 may then attempt to return to the source eNB 210 based on the RF conditions but may be using the incorrect configuration/parameters. For example, the target eNB 230 may assign a cell radio network temporary identity (C-RNTI) to the UE 220. If the UE 220 uses the target eNB's C-RNTI with the source eNB 210, the source eNB 210 may not be able to locate the correct UE context because the C-RNTI is an identity that is unique within an eNB (here the target eNB). This causes the reestablishment procedure to fail. This situation is described as a “Too Early Handover” problem.
Conventional techniques to deal with this “Too Early Handover” problem, focus optimizing the HO parameters in order to minimize the chances that the problem occurs. However, these techniques do not help to minimize the impact of failures that still manage to occur.
The occurrence of the problem with reestablishment procedures will tend to increase as the network has more ping pong scenarios along inter-eNB seams. As the network operators start deploying small cells, the inter eNB seams will increase. Thus, there is a risk that the IA/LCs in the network may increase.
What is needed is a technique to allow the source eNB to quickly locate the correct UE context in order to reduce connection delays and/or lost calls when a “Too Early Handover” problem occurs.